1. Technical Field
The present invention relates to a method for producing an organic acid using a bacterium such as a coryneform bacterium.
2. Background Art
For the production of non-amino organic acids, including succinic acid, by fermentation, anaerobic bacteria are typically used, including anaerobic bacteria belonging to the genus Anaerobiospirillum or Actinobacillus (U.S. Pat. No. 5,142,834, International Journal of Systematic Bacteriology, 49, 207-216 (1999)). Although such anaerobic bacteria provide high yields of products, many nutrients are required for their proliferation, and therefore it is necessary to add large amounts of organic nitrogen sources such as corn steep liquor (CSL) into the culture medium. The addition of large amounts of sources of organic nitrogen results in not only an increase in cost for the culture medium, but also an increase in the purification costs for isolating the product, and therefore it is not economical.
In addition, methods are known in which aerobic bacteria such as coryneform bacteria are cultured once under aerobic conditions to proliferate the bacterial cells, then the cells are harvested, washed, and allowed to rest so that a non-amino organic acid is produced without having to supply oxygen (Japanese Patent Laid-open (KOKAI) Nos. 11-113588 and 11-196888). When aerobic bacteria which were grown under aerobic conditions are used for the production of non-amino organic acids as described above, a culture under microaerobic conditions (also called “microaerobic induction”) is generally necessary to produce succinic acid under anaerobic conditions. These methods are economical, since organic nitrogen can be added in a smaller amount for proliferation of the bacterial cells, and the bacteria can sufficiently grow in a simple culture medium. However, there is still a room for improvement in terms of production amounts, concentration, and production rate per cell of the target organic acids, as well as simplification of the production process, and the like. Furthermore, techniques of increasing a non-amino organic acid-producing ability by DNA recombination have also been disclosed. For example, production of a non-amino organic acid by fermentation using a bacterium in which phosphoenolpyruvate carboxylase activity is enhanced (for example, Japanese Patent Laid-open No. 11-196887), and the like, have also been reported.
The entire genome sequence of a coryneform bacterium has been reported, and the functions of putative protein-coding sequences have been predicted (Appl. Microbiol. Biotechnol., 62 (2-3), 99-109 (2003)). The sucE1 gene is one of these putative protein-coding sequences, and although the gene is thought to code for a permease, the actual function has not been clarified. Finally, participation of the sucE1 gene in the succinic acid synthetic pathway was also not known. As for maleate dehydrogenase, although a method for producing succinic acid using a bacterium in which activity of this enzyme is enhanced has been reported (Japanese Patent Laid-open No. 2006-320208), the effect of enhancing the mdh gene along with the sucE1 gene has not been reported